1. Field of the Invention
The present invention relates to an apparatus for ejecting liquid, which is applicable to, for example, an ink jet type print head and a spraying/coating apparatus.
2. Description of the Background Art
FIG. 18 is a sectional view showing a structure of a conventional liquid ejector, which is introduced in Japanese Patent Application Laid-Open No. 10-278253, for example. A cavity is provided on an ink tank 10 for storing ink 30. The cavity communicates with an opening 19 opened on the ink tank 10 and has a parabolic reflecting wall 11 as an inner wall which locates a focal point 12 in the vicinity of the opening 19. The cavity is also opened at the opposite side of the opening 19, where a piezoelectric transducer 20 is provided to vibrate the ink 30. The vibration is carried out by connecting an ac source 25 between a surface of a piezoelectric vibration excitor 29 forming the piezoelectric transducer 20 and an electrode 21 for preventing leakage of the ink 30 from the cavity through wirings 24 and 23, respectively.
In such a liquid ejector, the vibration of the piezoelectric transducer 20 provides acoustic wave 26 for the ink 30 stored in the cavity in almost plane form. The acoustic wave 26 propagates within the ink 30 and reaches the reflecting wall 11 to be focused onto the focal point 12. Since the focal point 12 is positioned near the opening 19, the acoustic energy of the ink 30 at this point increases in density so that an ink droplet 31 is ejected.
A leading path 13 which supplies the ink 30 into the cavity is provided on the reflecting wall 11 and near the piezoelectric transducer 20 so as not to impair the function of reflecting the acoustic wave 26.
However, this arrangement easily causes an air bubble 30a to remain in the cavity, especially on the opposite side of the leading path 13 near the piezoelectric transducer 20 when the ink 30 is supplied from the leading path 13 into the cavity surrounded by the reflecting wall 11. The occurrence of the bubble 30a may impair the propagation of the acoustic wave 26 and the reflection at the reflecting wall 11 at the position, which may result in decrease in the acoustic energy at focusing. That is, it is a first problem that the presence of the bubble 30a makes it difficult to control a droplet to be ejected and worsens the ejection efficiency.
Since the focal point 12 is provided in the vicinity of the opening 19, the leading path 13 on the opposite side of the opening 19 is placed at a position where the reflecting wall 11 with a parabolic surface extends wide open. This causes a mechanism for supplying the ink to the leading path 13 to be provided outside the maximum diameter of the cavity, resulting in a second problem that is to be a factor of preventing miniaturization of the device.
A first aspect of the present invention is directed to a liquid ejector comprising at least one acoustic conductor for propagating acoustic wave including a first surface and an outer surface for reflecting the acoustic wave given to the first surface and focusing it onto a focal point. The liquid ejector further comprises a supplying path for supplying liquid to be ejected from the outside of the acoustic conductor to the focal point. The xe2x80x9coutside of the acoustic conductorxe2x80x9d indicates portions other than the acoustic conductor, and includes a form that the xe2x80x9coutsidexe2x80x9d is surrounded by the acoustic conductor.
According to a second aspect of the present invention, in the liquid ejector of the first aspect, in cross section of the at least one acoustic conductor, the outer surface presents a parabola having a focus on the focal point, and the acoustic wave is supplied in parallel with an axis of the parabola.
According to a third aspect of the present invention, in the liquid ejector of the first aspect, in cross section of the at least one acoustic conductor, the outer surface presents an ellipse having a first focus on the focal point, and the acoustic wave is supplied radially at a second focus of the ellipse.
According to a fourth aspect of the present invention, in the liquid ejector of the first aspect, the supplying path is arranged outside the outer surface.
According to a fifth aspect of the present invention, in the liquid ejector of the fourth aspect, the at least one acoustic conductor includes a plurality of acoustic conductors, and the supplying path is used in common for the plurality of acoustic conductors.
According to a sixth aspect of the present invention, in the liquid ejector of the fifth aspect, the supplying path extends in a direction that the plurality of acoustic conductors are arranged.
According to seventh and tenth aspects of the present invention, in the liquid ejector of the fourth or ninth aspect, the at least one acoustic conductor further comprises a second surface arranged closer to the first surface than the focal point, a boundary between the liquid to be ejected and the second surface is perpendicular to a traveling direction of the acoustic wave reflected at the outer surface.
According to eighth and eleventh aspects of the present invention, in the liquid ejector of the seventh or tenth aspect, in cross section of the at least one acoustic conductor, the outer surface presents a parabola having a focus on the focal point, and the second surface presents an arc shape being convex to the first surface.
According to a ninth aspect of the present invention, in the liquid ejector of the first aspect, the at least one acoustic conductor further comprises an inner surface separated from the outer surface, and the supplying path is formed by the inner surface.
According to a twelfth aspect of the present invention, in the liquid ejector of the eleventh aspect, in the cross section where the outer surface presents the parabola, an intersection of the first surface and the parabola is taken as a first intersection, an intersection of the arc and a line connecting the first intersection and the focus of the parabola is taken as a second intersection, and the inner surface is positioned closer to the axis than a line passing through the second intersection in parallel with the axis.
According to a thirteenth aspect of the present invention, in the liquid ejector of the ninth aspect, the outer surface presents a parabola in cross section having a focus on the focal point, and the inner surface is provided in the vicinity of an axis of the parabola.
According to a fourteenth aspect of the present invention, in the liquid ejector of the thirteenth aspect, the inner surface presents a line in cross section of the at least one acoustic conductor.
According to a fifteenth aspect of the present invention, in the liquid ejector of the ninth aspect, the at least one acoustic conductor is liquid being filled in between a body surrounding the at least one acoustic conductor and the supplying path.
According to a sixteenth aspect of the present invention, the liquid ejector of the first or fourteenth aspect further comprises a protecting member being in contact with the outer surface of the at least one acoustic conductor and having an acoustic impedance larger than that of the at least one acoustic conductor.
According to a seventeenth aspect of the present invention, in the liquid ejector of the sixteenth aspect, the protecting member is thicker than the wavelength of the acoustic wave in the at least one acoustic conductor.
According to an eighteenth aspect of the present invention, in the liquid ejector of the first aspect, the outer surface has a diameter decreasing from the focal point toward an opening for ejecting the liquid to be ejected.
In the liquid ejector of the first to third aspects, focusing of the acoustic wave results in increase in the acoustic energy to eject the liquid to be ejected. Further, there is no need to provide an inner wall combining the function of storing the liquid to be ejected with that of reflecting the acoustic wave, so that the liquid to be ejected is not supplied into a cavity formed by such an inner wall. Accordingly, an air bubble hardly appears in the liquid to be ejected.
In the liquid ejector of the fourth aspect, liquid is provided from the outside of the outer surface, which makes it easy to form a supplying path where an air bubble hardly appears.
The liquid ejector of the fifth aspect allows a general supply of the liquid to be ejected to the plurality of acoustic conductors. Further, the components are used in common, which results in reduction in the number of parts and easy assemble. Therefore, the cost can be reduced.
The liquid ejector of the sixth aspect is capable of supplying the liquid to be ejected to the plurality of acoustic conductors rapidly and smoothly without an air bubble remained.
In the liquid ejector of the seventh or tenth aspect, the reflection of the acoustic wave is small at the boundary between the acoustic conductor and the liquid. Thus, the focusing efficiency of the acoustic energy in the liquid can be increased.
In the liquid ejector of the eighth or eleventh aspect, the boundary between the acoustic conductor and the liquid is perpendicular to the traveling direction of the reflected acoustic wave, resulting in minimization of the reflection at the boundary. Moreover, the acoustic wave is in phase at the focal point, so that the Focusing efficiency of the acoustic energy in the liquid to be ejected is increased.
In the liquid ejector of the ninth aspect, the liquid to be ejected is supplied from the inner surface of the acoustic conductor. This allows to avoid size increase of the liquid ejector which will be caused by providing a liquid supplying mechanism. In addition, its weight can be reduced.
In the liquid ejector of the twelfth aspect, every acoustic wave reflected at the outer surface can be made incident perpendicularly to the liquid.
In the liquid ejector of the thirteenth aspect, the supplying path is provided in the vicinity of the axis of the parabola which makes a minor contribution to the reflection of the acoustic wave.
In the liquid ejector of the fourteenth aspect, since the supplying path has a simple form, an air bubble is hardly produced.
In the liquid ejector of the fifteenth aspect, the acoustic impedance of the liquid to be ejected and that of the acoustic conductor can be approximated to each other, so that the ejection efficiency is improved.
The liquid ejector of the sixteenth aspect maintains the function of the outer surface of reflecting the acoustic wave propagating in the acoustic conductor while preventing the function of the acoustic conductor of propagating the acoustic wave from outside disturbances.
The liquid ejector of the seventeenth aspect suppresses transmission of the acoustic wave given to the first surface into the protecting member from the outer surface.
The liquid ejector of the eighteenth aspect is capable of further reducing the focusing diameter to eject the liquid to be ejected even when the acoustic wave has a long wavelength in the acoustic conductor and a large focusing diameter at the focal point.
An object of the present invention is to provide a liquid ejector in which the arrangement of a leading path for supplying liquid such as ink has been devised in order to solve the above first or second problem.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.